draft-duric-rtp-ilbc-00 emai/ SIP: alan.duric@globalipsound.com - - PowerPoint PPT Presentation

draft-duric-rtp-ilbc-00

emai/ SIP: alan.duric@globalipsound.com

iLBC - IETF work

• IETF deliverables, submitted during February ‘02:

– iLBC codec specification draft

• experimental

standards track – iLBC RTP Payload Profile

• regular standards

track (AVT) – Statement about IPRs in ILBC and its “freeware nature”

• Dynastat results submission to the AVT mailing list

iLBC (internet Low Bitrate Codec)

• Speech sampled at 8 kHZ,
• using a block-independent linear-predictive coding (LPC)

algorithm.

• Bandwidth 13.967 kbps (53 bytes per 30 ms)
• Frame size 30 ms (support for 20 ms in the next revision)
• Complexity and memory requirements are similar to ITU

G.729A

• Basic Quality is equal to or better than G.729. Packet loss

robustness is significantly better than G.729.

• Packet loss concealment - Integrated example solution

Why iLBC !?

• Current low bit rate codecs: ITU G.729, G.723.1, GSM-EFR, and

3GPP-AMR were developed for circuit switched & wireless telephony and are all based on the CELP (Code Excited Linear Prediction) paradigm.

• CELP coders are stateful, they have memory, error propagation

results from lost or delayed packets.

• iLBC treats every packet individually, making it suitable for

packet communications.

Transport of iLBC frames

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ : contributing source (CSRC) identifiers | |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | | | One or more iLBC frames | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Storage mode

Header Speech Frame 1 Speech Frame n :

• The file begins with a header that includes only a magic number

to identify that it is an iLBC file.

• The magic number for iLBC file MUST correspond to the ASCII

character string "# !iLBC\ n", or "0x23 0x21 0x69 0x4C 0x42 0x43 0x0A" in hexadecimal form.

SDP parameters

m = < m edia> < port> < transport> < payload list> < m edia> application < port> is the port num ber < transport> RTP/ AVP < payload list> dynam ic payload num ber a = rtpm ap:< payload> < encoding nam e> < payload> is the dynam ic payload num ber < encoding nam e> iLBC indicates iLBC stream . Exam ple: m = audio 4 9 1 2 0 RTP/ AVP 9 7 a = rtpm ap:97 iLBC

MIME Type registration

MIME media type name: audio MIME subtype: iLBC Optional parameters: maxptime: The maximum amount of media which can be encapsulated in a payload packet, expressed as time in milliseconds. The time is calculated as the sum of the time the media present in the packet represents. The time MUST be a multiple of the frame size of RTP packet.